VP9 is an open source, royalty free video codec. It is developed by Google to provide a free alternative to things like H264 and H265. Implementing codecs for both of those require paying licence fees.

Codecs can be in software, but can also be implemented in hardware which is much more power efficient. This change enables the Linux kernel to use hardware VP9 decoders so that software can decode (play) VP9 video much more efficiently when that hardware is available.